The invention relates to a reflective flat-panel color display device having a display panel which comprises a diffusing liquid crystalline material present between a first and a second substrate, the display device including a color filter.
A display panel as used in the color display device of the type described in the opening paragraph is known from, for example the English-language abstract of JP-A 59-10924. This document describes a flat-panel reflective display device in which a dichroic reflector is arranged under the optically active layer. A diffusing and reflecting plate is arranged outside the display panel. The dichroic reflector is transmissive to green light and reflective to red and blue light. When a white beam is incident on the display device and when the liquid crystalline material is in its diffuse state, then red and blue are diffused in the layer and subsequently reflected by the dichroic reflector. They return as diffuse light. Green light is also diffused in the layer and passed by the dichroic reflector to the next reflector. Reflection and diffusion take place on this reflector so that also the green beam returns as a diffuse beam. For the viewer, the display device is in the bright state. When a white beam is incident on the display device and when the layer is in the transparent state, then red and blue light will be reflected on the dichroic mirror without being diffused. The green light is passed and reflected on the diffusing reflector. The green light thus returns in a diffuse state. The viewer now watches a green monochrome display panel.
A drawback of the display device known from the abstract is that an artefact occurs when this configuration is used for a three-color panel. Namely, a transparent pixel will produce a light spot on the diffusing reflector. The edges of this light spot will be visible to the viewer through neighbouring transparent pixels, so that the viewer will observe ghost images. A further drawback is that the diffuser mentioned in this document diffuses through 180.degree.. This light will be enclosed in the substrate until it reaches a pixel with a color filter passing the relevant color to the liquid crystalline layer. However, in this way, a part of this light will not be coupled out when it reaches the sides of the display panel so that this part will be lost. When, for example a pixel is blue in the transparent state, it will be light yellow instead of white in a diffuse state, due to loss at the sides.